Extruded 1XXX-series aluminium alloy tube product

ABSTRACT

An aluminum alloy extruded tube product for a heat exchanger assembly and made from an 1xxx-series aluminum alloys and including furthermore a purposive addition of one or more wetting elements selected from the group of: Bi 0.03% to 0.5%, Pb 0.03% to 0.5%, Sb 0.03% to 0.5%, Li 0.03% to 0.5%, Se 0.03% to 0.5%, Y 0.03% to 0.05%, Th 0.03% to 0.05%, and the sum of these elements being 0.5% or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a §371 National Stage Application of International ApplicationNo. PCT/EP2012/056013 filed on 3 Apr. 2012, claiming the priorities ofEuropean Patent Application No. 11163391.3 filed on 21 Apr. 2011 andU.S. Patent Application 61/478,155 filed on 22 Apr. 2011.

FIELD OF THE INVENTION

The invention relates to an extruded aluminium alloy tube product. Morespecifically this invention discloses aluminium tube products used inthe manufacture of heat exchangers. The invention further relates to amethod for manufacturing a heat exchanger assembly incorporating anextruded aluminium alloy tube product.

BACKGROUND TO THE INVENTION

As will be appreciated herein below, except as otherwise indicated,aluminium alloy designations and temper designations refer to theAluminium Association designations in Aluminium Standards and Data andthe Registration Records, as published by the Aluminium Association in2010 and are well known to the person skilled in the art.

For any description of alloy compositions or preferred alloycompositions, all references to percentages are by weight percent unlessotherwise indicated. The term “up to” and “up to about”, as employedherein, explicitly includes, but is not limited to, the possibility ofzero weight-percent of the particular alloying component to which itrefers. For example, up to about 0.1% Zn may include an alloy having noZn.

Heat exchangers and other similar equipment, such as condensers,evaporators and the like for use in car coolers, air conditioningsystems, industrial cooling systems, etc. usually comprise a number ofheat exchange tubes arranged in parallel between two headers, each tubejoined at either end to one of the headers. Corrugated fins are disposedin an airflow clearance between adjacent heat exchange tubes and arebrazed to the respective tubes.

The tubes or refrigerant tubes are being manufactured for example byfolding a brazing sheet clad on the outside with a brazing materiallayer.

Alternatively the tubes are produced by means of extrusion. Typicalextrusion based heat exchangers come essentially in two designs. Thefirst design uses round tubing and fins that are mechanically attachedto the round tubes by first lacing the tubes into holes punched in thefins, and then expanding the tubes to ensure that the tube's outersurface is in close mechanical contact with the fins.

The second typical design uses flat tubing or flat tubes having aplurality of channels in the tubing, commonly referred to as multi-voidtubing or micro multi-void tubing or or multi port extruded tubes ormulti-cavity tubing or multi-porthole tubing. This type of heatexchanger tubing is attached to the fins using a brazing process. Thecross section of the flow channels can vary, e.g. circular, oval,square, rectangular, or other regular or irregular shapes. Typically,micro multi-void and multi-void tubing are about 10-80 mm in width andabout 1-5 mm in height.

For the extruded multi-void tubing a wide variety of aluminium alloysare employed. The AA1000-series aluminium alloys are often selectedwhere corrosion resistance is needed. Where higher strengths arerequired, the AA3000 and AA6000-series are often used. There are variousdisclosures of aluminium alloys for use in micro multi-void andmulti-void tubing and whereby the alloy composition has been optimisedto meet specific improvements in corrosion resistance or strengthlevels.

There is room for improvement in the art of aluminium extruded alloytube stock for brazed heat exchangers and for methods of manufacturingsuch brazed heat exchangers, in particular for brazing methods that donot require the application of a brazing flux material.

DESCRIPTION OF THE INVENTION

It is an object of the invention to provide an aluminium alloy extrudedtube stock material for brazed heat exchangers for use in particular forbrazing methods that do not require the application of a brazing fluxmaterial.

This and other objects and further advantages are met or exceeded by thepresent invention and providing an aluminium alloy extruded tube productfor a heat exchanger assembly and made from an AA1xxx-series aluminiumalloy and comprising furthermore a purposive addition of one or morewetting elements selected from the group consisting of: Bi 0.03% to0.5%, Pb 0.03% to 0.5%, Sb 0.03% to 0.5%, Li 0.03% to 0.5%, Se 0.03% to0.5%, Y 0.03% to 0.05%, Th 0.03% to 0.05%, and the sum of these elementsbeing 0.5% or less.

The wetting elements are selected from the group consisting of Bi, Pb,Li, Sb, Se, Y, and Th, and wherein the total amount of the wettingelement(s) is in a range of about 0.01% to 0.5%. Preferably the totalamount of wetting element(s) does not exceed 0.4%.

In accordance with the present invention it has been found that thisinvention allows for the manufacture of brazed assemblies incorporatingaluminium workpieces including the aluminium alloy extruded tube andwhereby there is no demand to provide a brazing flux material, like afluoride flux, in a controlled atmosphere brazing process. During thebrazing cycle the subject wetting agent at or near the extruded productsurface region and that diffuses from the extruded product to thesurface region into the molten aluminium-silicon filler alloy used tobraze the extruded tube stock to the other components, such as fins andheaders, and whereby the wetting agent facilitates a good flowability ofthe molten filler alloy such that in a controlled atmosphere brazingprocess a good fillet formation is being obtained, even without the useof a flux material.

It is known in the art that during controlled atmosphere brazing incombination with a brazing flux material, for example a fluoride basedflux, the Mg level in the aluminium alloys should be kept at a lowlevel, typically less that 0.2%, and more preferably of less than 0.05%,to avoid any detrimental interaction between the Mg and the flux. Inaccordance with the present invention it has been found that since theextruded aluminium alloy tubes material is ideally suitable for fluxlessbrazing in a controlled atmosphere brazing operation, there is acorresponding tolerance for Mg in the aluminium alloy. For that reasonMg can be tolerated at significantly higher levels or it can be addedpurposively. As set out hereinafter, another purposive role for Mg isthat it may favourably interact with the wetting agent applied, inparticular when Bi is being used.

In a preferred embodiment the element Bi is selected from this group ofwetting elements and is in a range of about 0.03% to 0.5%, andpreferably in a range of about 0.03% to 0.35%, and a more preferredupper-limit is 0.30%, as being the most efficient wetting element forthis purpose in these aluminium alloy systems during a controlledatmosphere brazing operation. A preferred lower limit for the Biaddition is 0.06%. Typically Bi levels are about 0.1% and about 0.15%.

In the embodiment that Bi is added, and preferably solely Bi is beingadded, to the aluminium alloy extruded tube it is further preferred thatthe excess Mg content with respect to the stoichiometric composition ofBi₂Mg₃ is 0.1% or less, and preferably 0.07%. It has been found that Bihas a low solubility in aluminium and tends to separate out at the grainboundaries even when added at low levels of for example 0.1% or 0.15%.This can result in an undesirable white dusty appearance of the extrudedtube when kept on stock for a long period of time. To overcome thiseffect a small amount of Mg will form Bi₂Mg₃ which stops separation atthe grain boundaries. This Bi₂Mg₃ phase will however dissolve in thealuminium alloy upon heating during a brazing cycle and releasing the Bito lower the surface tension of the molten AlSi filler.

The extruded aluminium alloy is preferably free of each of the elementsNa, Li, K, and Ca to avoid any interference with the Bi and any optionalMg during the controlled atmosphere brazing operation. With “free” ismeant that no purposeful addition of Na, Li, K, and Ca was made to thechemical composition but that due to impurities and/or leaking fromcontact with manufacturing equipment, trace quantities of Na, Li, K, andCa may nevertheless find their way into the filler alloy product. Forexample, less than 0.006% is an example of a trace quantity.

In an embodiment of the invention the extruded tube the aluminium alloymay further comprise Mg up to about 0.3%.

Preferred alloys are those having a composition within the ranges of1050, 1060, 1100, 1110, 1300, 1350, 1350A, 1370, and 1235. Preferredconditions are the F, O, H111, and H112 tempers.

In another aspect of the invention there is provided a method ofmanufacturing an article, a heat exchanger, joined by brazing or anassembly of brazed components, comprising the steps of:

(a) providing or forming the components to be brazed together of whichat least one is made from an extruded aluminium alloy tube product, inparticular a multi-porthole tube, according to this invention;

(b) assembling the components, the multi-porthole tube and othercomponents such as fins, into an assembly;

(c) brazing the assembly without applying a brazing flux on the assemblyof components, and brazing the whole assembly in a controlled inert gasatmosphere at a brazing temperature, typically at a temperature in arange of about 540° C. to 615° C., e.g. about 600° C. or about 590° C.,for a period long enough for melting and spreading of a brazingmaterial, preferably an Al—Si alloy brazing material, joining thevarious components including the extruded tube product and fins, e.g. adwell time of 2 to 5 minutes, typically at around 2 or 3 minutes; andwhereby typically the oxygen content in the brazing atmosphere should beas low as reasonable possible, and is preferably below about 200 ppm,and more preferably below about 100 ppm, for example at 15 ppm or less;

(d) cooling of the brazed assembly, typically to below about 100° C.,e.g. to ambient temperature.

For the purposes of this invention, and as used herein, the term“controlled atmosphere brazing” or “CAB” refers to a brazing processwhich utilizes an inert atmosphere, for example, nitrogen, argon orhelium in the brazing of aluminium alloy articles, and is distinct fromvacuum brazing in particular in that with CAB the brazing atmosphere inthe furnace during the brazing operation is at about regular atmosphericpressure, although a slight under-pressure (for example working at apressure of about 0.1 bar or more) or having a slight over-pressure canbe used to facilitate the control of the inert gas atmosphere and toprevent an influx of oxygen containing gas into the brazing furnace.

While various embodiments of the technology described herein have beendescribed in detail, it is apparent that modifications and adaptationsof those embodiments will occur to those skilled in the art. However, itis to be expressly understood that such modifications and adaptationsare within the spirit and scope of the presently disclosed technology.

The invention claimed is:
 1. A method of manufacturing an article joinedby brazing or an assembly of brazed components, comprising the steps of:(a) forming the components of which at least one is made from anextruded aluminium alloy tube product, made from an AA1xxx-seriesaluminium alloy selected from the group of: 1050, 1060, 1100, 1110,1300, 1350, 1350A, 1370 and 1235, and comprising furthermore a purposiveaddition of one or more wetting elements selected from the groupconsisting of: Bi 0.03 wt % to 0.5 wt %, Pb 0.03 wt % to 0.5 wt %, Sb0.03 wt % to 0.5 wt %, Li 0.03 wt % to 0.5 wt %, Se 0.03 wt % to 0.5 wt%, Y 0.03 wt % to 0.05 wt %, Th 0.03 wt % to 0.05 wt %, and the sum ofthese elements being 0.5 wt % or less, wherein the alloy is free of eachof the elements Na, Li, K and Ca, (b) assembling the components into anassembly, (c) brazing the assembly without applying brazing flux on theassembly of components and brazing the whole assembly in an inertcontrolled gas atmosphere at a brazing temperature to form a brazedassembly, and (d) cooling of the brazed assembly.
 2. The methodaccording to claim 1, wherein the AA1xxx-series aluminium alloyscomprise one or more said wetting elements selected from the groupconsisting of: Pb 0.03 wt % to 0.5 wt %, Sb 0.03 wt % to 0.5 wt %, Li0.03 wt % to 0.5 wt %, Se 0.03 wt % to 0.5 wt %, Y 0.03 wt % to 0.05 wt%, Th 0.03 wt % to 0.05 wt %, and the sum of these elements being 0.5 wt% or less.
 3. The method according to claim 1, wherein the AA1xxx alloysfurther comprise Mg.
 4. The method according to claim 3, and wherein theAA1xxx alloys comprise Mg and 0.03 wt % to 0.5 wt % Bi, and wherein theexcess Mg content with respect to the stoichiometric composition ofBi₂Mg₃ is 0.1 wt % or less.
 5. The method according to claim 1, whereinthe AA1xxx alloys comprise solely a purposive addition of Bi in a rangeof 0.03 wt % to 0.5 wt %.
 6. The method according to claim 1, whereinthe AA1xxx-series aluminium alloy is an alloy selected from the groupof: 1050, 1060, 1100, 1110, 1300, 1350, 1350A, 1370, and
 1235. 7. Themethod according to claim 1, wherein the extruded tube is in a conditionselected from the group of: F, O, H111, and H112 temper.
 8. The methodaccording to claim 1, wherein the assembly is a heat exchanger assembly,wherein the tube is a multi-porthole tube of the heat exchangerassembly.
 9. The method according to claim 1, wherein the AA1xxx-seriesaluminium alloy comprises 0.03 wt % to 0.30 wt % Bi is present.
 10. Themethod according to claim 1, wherein the AA1xxx-series aluminium alloycomprises 0.063 Wt % to 0.5 wt % Bi.
 11. The method according to claim10, wherein the extruded aluminium tube product is a multi-portholetube.
 12. The method according to claim 10, wherein during step (c) thebrazing temperature is in the range of 540° C. to 615° C.
 13. The methodaccording to claim 10, wherein during step (c) the oxygen content in theinert controlled gas atmosphere is below 200 ppm.
 14. The methodaccording to claim 1, wherein the AA1 xxx-series aluminium alloycomprises solely a purposive addition of Bi in a range 0.03 wt % to 0.35wt %.
 15. The method according to claim 10, wherein during step (c) theoxygen content in the inert controlled gas atmosphere is below 100 ppm.16. The method according to claim 10, wherein during step (c) the oxygencontent in the inert controlled gas atmosphere is less than 15 ppm. 17.The method according to claim 1, wherein the AA1xxx-series aluminiumalloy is an alloy selected from the group of: 1110, 1350, 1350A, and1370.
 18. A method of manufacturing an article joined by brazing or anassembly of brazed components, comprising the steps of: (a) assemblingthe components into an assembly, said components comprising at least afirst component and a second component, wherein said first component isa tube, and said first component consists of extruded AA1xxx-seriesaluminium alloy selected from the group of: 1050, 1060, 1100, 1110,1300, 1350, 1350A, 1370 and 1235, and comprising furthermore a purposiveaddition of one or more wetting elements selected from the groupconsisting of: Bi 0.03 wt % to 0.5 wt %, Pb 0.03 wt % to 0.5 wt %, Sb0.03 wt % to 0.5 wt %, Li 0.03 wt % to 0.5 wt %, Se 0.03 wt % to 0.5 wt%; Y 0.03 wt % to 0.05 wt %, Th 0.03 wt % to 0.05 wt %, and the sum ofthese elements being 0.5 wt % or less, wherein the alloy is free of eachof the elements Na, Li, K and Ca, (b) brazing the assembly withoutapplying brazing flux on the assembly of components and brazing thewhole assembly in an inert controlled gas atmosphere at a brazingtemperature to form a brazed assembly, and (c) cooling of the brazedassembly.
 19. The method according to claim 18, wherein cooled brazedassembly is a heat exchanger, wherein during step (b) the oxygen contentin the inert controlled gas atmosphere is below 200 ppm.
 20. The methodaccording to claim 18, wherein the AA1xxx-series aluminium alloy is analloy selected from the group of: 1110, 1350, 1350A, and 1370.